1. Field of the Invention
The present invention relates generally to video display monitors and more particularly to a method for adjusting image geometry in a video display monitor.
2. Description of the Background Art
The display of high quality images is a primary concern of manufacturers, developers and users of video display monitors. Over the operational lifetime of a video display monitor, it may become desirable or necessary from time to time to make adjustments to the geometry of the image displayed by the monitor. Such adjustments may be required to compensate for a degradation or drift in the performance of monitor components. Alternatively, geometry adjustments may be effected to accommodate the individual preferences of the user. Geometry adjustments may also be made to compensate for variations in the direction and magnitude of the local ambient magnetic field, which depends upon, among other factors, the geographical location at which the monitor is being used.
With reference to FIG. 1, there is depicted a cathode ray tube (CRT) video display monitor 10 of a type commonly used in connection with computer systems. The monitor 10 includes a transparent screen 12 having an inner surface that is covered with a phosphor coating 14. An electron gun 16 is configured to emit a beam of electrons 18 directed toward the screen 12. At least one magnetic coil 20 continuously redirects the path of electron beam 18 such that the locations at which electrons impinge on the phosphor coating 14 (which emits light in response to such impingement) is controlled and the desired image is produced on the screen. The display monitor 10 may include an aperture grill 22 which selectively directs electrons to red, green and blue light emitting phosphors to thereby produce a composite color image.
Adjustment of image geometry in a CRT video display of the foregoing description is generally accomplished by modifying the operation of the magnetic coil 20, which in turn changes the pattern of electron impingement on phosphor coating 14. A known method for adjusting image geometry utilizes positional information received from an input device, such as a mouse or trackball, to modify magnetic coil operation accordingly. The method may typically include the step of generating an image geometry adjustment screen having objects which may be spatially manipulated by the appropriate operation of the input device. The movement of the input device is then used to modify the magnetic deflection operational parameters such that the relevant aspect of the image geometry is adjusted by an amount proportional in some manner to the direction and magnitude of the input device movement. During the spatial manipulation of the geometry adjustment object or indicia and associated adjustment of the screen geometry, the position of the input device is continuously visually represented on the screen at by an input device pointer.
When a user makes adjustments to image geometry according to the above method, the movement of the input device pointer displayed on the monitor and viewed by the user is a combined result of the movement of the input device and of the change in image geometry produced by the input device movement. This may tend to produce an exaggeration or other anomaly of the movement of the input device pointer with respect to the movement of the input device. For example, a small movement of the input device may result in a disproportionately large movement of the input device pointer on the screen. This exaggeration of input device pointer movement will generally be disorienting to the user and will render the task of making precise adjustments of image geometry difficult or impossible. While the perceived exaggeration may be alleviated somewhat by reducing the size of the image adjustment screen, such a reduction will reduce the precision to which geometry adjustment may be performed. Therefore, there remains a need for a method of adjusting screen geometry of a video display monitor which overcomes the above-described problems.